The proposed experiments will measure the plastic responses of a highly conserved neuroendocrine circuit necessary for reproduction using an ideally suited model system, the African cichlid fish, Astatotilapia burtoni. In male A. burtoni, social status regulates reproduction via gonadotropin releasing hormone (GnRH1) neurons in the pre-optic area of the brain. The size, dendritic extent and activity of these neurons increase in dominant, reproductively active males and decrease in non dominant males. These social status-induced changes in GnRH1 neurons are well known, however the functional changes that occur during this social conversion are not. To map the functional changes, I will trace neuronal inputs to GnRH1 neurons, comparing those of sexually competent dominant males with those of sexually immature non dominant males. I will also perform a high resolution histochemical analysis of neurotransmitters that influence GnRH1 neurons in each type of male. I will use a novel new technique, array tomography, that allows repeated immunocytochemical labeling on the same brain sections. Understanding the neural plasticity induced by social status change in this uniquely suited model organism will identify the mechanism through which social behavior controls neuronal plasticity of the reproductive system. Sexual maturation is an important biological development that prepares an organism for reproductively active adult life stages. The brain integrates complex social and environmental information to initiate and manage the neural and hormonal changes that support this event. As the GnRH1 system controls reproductive output and fertility in all vertebrates, including humans, understanding the mechanisms that control plastic changes in the reproductive structures of the brain may lead to improved therapies for reproductive disorders, and improve public health.